1. Field of the Invention
The present invention relates to a rotary compressor, particularly to a variable-delivery vane-type rotary compressor which is used as a refrigerant compressor for an air conditioner for a vehicle or the like.
2. Description of the Background Art
Generally, in order to control discharge in vane-type rotary compressor, a suction port being in communication with the interior of a cam ring is provided on a side-block which covers one end of the cam ring and the position of the suction port is changed, so that the starting position of compression caused by rotation of the vanes is changed.
For example, a variable-delivery vane-type rotary compressor, which is a background art of the present invention, includes an arc-shaped by-pass port, which is provided in a front plate so as to extend beside the cam surface of a cam ring, the end opening of which may open on any radial section of a working chamber, and a rotatable disc having an arc-shaped opening between the front plate and the cam ring. In this compressor, the rotatable disc may rotate by means of an electric motor provided within or outside the compressor so as to change the position of by-pass opening in order to control discharge.
However, since the rotatable disc having a by-pass opening is provided in addition to the front plate in this compressor in order to control the area of the by-pass port, there are disadvantages in that the compressor has a complicated construction, is relatively heavy and is expensive to manufacture.
The Japanese Patent First Publication (Jikkai) Showa 59-76786 discloses a variable-delivery vane-type rotary compressor which includes a suction opening provided in a front plate, the end opening of which is in communication with a working chamber, and a rotatable disc provided between the front plate and a rotor. The rotatable disc is provided with a suction port which is in communication with the suction opening. By rotating the rotatable disc about the axis of the rotor, the opened area of the suction port is changed, so that discharge of the compressor can be controlled.
However, since the rotatable disc is provided between the front plate and the rotor in this compressor, the rotatable disc is biased toward the front plate due to thrust load P of the rotor, i.e. P =D.sup.2 .times..pi./4.times..DELTA.P in which D is the diameter of the shaft of the rotor and .DELTA.P is the difference between opposing pressures applied to the opposite ends of the shaft. Therefore, it is difficult for the rotatable disc to rotate smoothly since friction force between the rotatable disc and the front plate is increased. As a result, since the driving force required for drving the rotatable disc is increased, there is a disadvantage in that the parts which actuate the rotatable disc become large, so that the overall weight of the compressor is increased.